1. Field of the Invention
The present invention relates to ultrasonic detection and, more specifically, to a device for enhancing ultrasonic detection.
2. Description of the Prior Art
Currently, the most common method of diagnosing breast cancer is X-ray mammography. Although it is often effective, it uses ionizing radiation, which has an inherent risk to the tissues being examined. Ultrasound detection is also used in breast examination. Ultrasound detection is based on differences in sound velocity in normal and abnormal tissues. However, it has a low probability of detecting many non-palpable tumors. Magnetic resonance imaging has also been used, but requires sophisticated and expensive equipment.
Exposing materials such as tissues to electromagnetic radiation causes the tissues to exhibit changes in acoustic properties as a result of photonic absorption and subsequent local heating. Spectrochemical techniques such as laser-induced fluorescence have previously been used to detect malignant tumors in vivo (see, e.g., U.S. Pat. No. 5,579,773, the disclosure of which is incorporated herein by reference). Certain tissues, such as tumors, exhibit greater changes in acoustic properties than in surrounding tissues. It has also been discovered that exposing tissues to modulated or pulsed light may also cause the generation of acoustic waves in the tissue, a process often referred to as the photo-acoustic effect. In photo-acoustic detection, intensity-modulated light or pulsed light is allowed to diffuse into a specimen and photons are absorbed, inducing energy level transitions in chemical and biological compounds. When the energy levels return to their de-excited ground state, some of the energy is transformed into kinetic energy or heat. The intensity modulation of the incident radiation produces a coherent modulation of the temperature of the material that, due to thermal expansion, generates a periodic pressure fluctuation of the same frequency. This pressure fluctuation, or acoustic signal, can be detected with a microphone or transducer in contact with the material being examined.
Photo-acoustic spectroscopy has been successfully performed on a variety of biological materials (see, e.g., Rosencwaig, A., Photo-acolistics and Photo-acotistic Spectroscopy, Wiley, New York, 1980). Studies of whole blood have been performed, in which conventional absorption spectroscopy has failed due to excessive light scattering. Other examples include: Photo-acoustic spectroscopy of chlorophyll within the intact green leaf and the detection of plant pathology; analysis of the biochemical characteristics of marine algae and phytoplankton and studies of the photochemical mechanisms of these organisms; the monitoring of bacteria in various stages of development; the effect of different commercial sun screens on human epidermal tissue; studies of human eye cataracts, and the detection of protein structural changes in rat epidermal tissue during postpartum maturation.
Many conventional analytical techniques (e.g., chromatography, fluorometry, spectrophotometry) are effective when applied to solutions of extracted biochemical compounds, Photo-acoustic spectroscopy has been shown to be effective in the biochemical characterization of intact and complex biological systems, such as intact cells and tissues.